Why Vitamin D is Key for Muscle Health

Why vitamin D matters for your musculoskeletal and overall health.

Supplement culture is full of grifters. And there is a highly problematic trend of licensed healthcare professionals (ostensibly bound by a code of ethics) hocking their Thorne labs affiliate links to top off their personal income at unneeded expense to patients. 

But there is one (extremely affordable) supplement that I actively encourage my patients to take -- at least during the winter. 

This time of year, in the latitude of Washington, DC, none of us can expose ourselves to enough sunlight to manufacture Vitamin D. 

The sun must be 50 degrees above the horizon in order for its UV-B rays to penetrate the atmosphere and reach ground level in an effective dose.  

What's more, many modern Americans have 9-5 type jobs that don't allow for meaningful mid-day outdoor time when the sun IS over 50 degrees from the horizon -- even near the summer solstice.

Vitamin D and Me. 

In late winter about 12 years ago, I requested my Vitamin D levels be tested at a regular medical check up. (Vitamin D is not included in the standard blood test panel that is commonly performed at check-ups).

I had a hunch mine was low. 

Perhaps because I read that 42% of the US population was Vitamin D deficient. I was curious if I was amongst that group. 

I was also experiencing common symptoms like tiredness, aches and pains, brain fog and a bit of overall sluggishness. Was it the long hours I was working while juggling a new career in physical therapy -- while also trying to remain a vigilant student of and teacher of yoga?

Maybe. But my blood test results were abysmal:

My Vitamin D level was 17 ng/mL. The laboratory "normal" range is (typically -- it can vary lab to lab and also vary by data interpretation) 30-60 ng/mL. 

I took my prescription strength, once a week, massive Vitamin D dose and it changed my life. I felt more energy immediately.

(And, yes, in the years since, I have create much better work-life-sleep balance). 

Vitamin D and Thee.

Since then, I have better understood the vital role of Vitamin D in overall wellbeing. 

Vitamin D is a keystone hormone in the body. It is essential for:

  • Maintaining and building bone density (promotes calcium absorption in the gut and is required for adequate serum calcium and phosphate concentrations to enable normal bone mineralization),
  • General bone growth and bone remodeling (due to the role of Vitamin D in osteoblasts and osteoclasts), 
  • Prevention of "hypocalcemic tetany" i.e. cramps and spasms (in theory this could include high daily levels of muscle tension, a common complaint my patients have), 
  • Reduction of inflammation, 
  • General cell growth (crucial for repair of injured tissues), 
  • Neuromuscular functions (nerve health is muscle health!),
  • Immune functions,
  • Glucose metabolism (diabetes prevention),
  • ...and much more.

Vitamin D plays a role in encoding proteins that regulate cell proliferation, differentiation, and apoptosis (cell death) -- exactly the mechanisms involved in cancer spread. 

Osteopenia and osteoporosis are inevitable without sufficient vitamin D (and calcium). Bones can become thin, brittle, soft or misshapen.

Many tissues in the body have vitamin D receptors.

And so you see...

I cannot -- in good faith -- talk with women over 40 about the need for resistance training for healthy bones without also mentioning Vitamin D. (This is due to the changes in hormones in peri- and post-menopause that decrease the ease with which our bones maintain their density).  

I cannot -- in good faith -- talk with a cancer survivor of any sort without also mentioning Vitamin D. 

I cannot -- in good faith -- talk with a patient who continues to injure themselves in innocuous activities without mentioning Vitamin D.

I cannot -- in good faith -- fully address someone's musculoskeletal issues knowing that their demanding job keeps them indoors during the sun's "D window" at least 5 days a week and they are not already supplementing with Vitamin D.   

You get the idea. 

I am not a medical doctor, and I do not pretend to be one. I do not run labs myself or prescribe anything but movement. 

But in our overwhelmed health care system, it matters that the people who get to spend the most time with patients and who also get to know their lifestyles (physical therapists), that we speak up about other simple, cost effective ways to improve their health.  

How to get a handle on your Vitamin D Levels 

DMinder app

The number one tool I recommend is not a supplement at all, but an app. The DMinder app is a sun<>skin tracking tool that I first learned about from Amy Ippoliti. (Amy lives in sunny Boulder Colorado, is frequently outdoors, is relatively fair skinned, and STILL discovered she was D deficient). 

The app takes basic data like your skin tone, whether you take a D supplement, and how much clothing you are wearing to roughly measure the amount of Vitamin D your body is likely making. It also tells you when your skin will burn and when to turn over if you are tanning.  

Get Tested

Download the app either way, so you can get a sense of your daily baseline doses (seasonally dependent), then ask your doctor for a 25-hydroxy vitamin D test, or 25-OH vitamin D test; Calcidiol; or 25-hydroxycholecalciferol test. 

If you don't want to go through the rigamarole of setting up an appointment, here is an at home Vitamin D test

Vitamin D3 supplement

Vitamin D3 is the recommended form of Vitamin D to take in supplement form. Ideally it is taken with vitamin K2. The two work synergistically to maintain bone health. Here's the supplement that I take.  

Vegan Vitamin D3

Vitamin D2 is always vegan, but vitamin D3 is not always vegan. This brand is vegan

If you have been struggling with a muscle injury, and have not had your vitamin D levels checked, I hope you take the actions outlined in this blog post. 


Much of the data in this post is derived from the following sources:

Vitamin D Fact Sheet for Health Professionals from the Office of Dietary Supplements at the National Institutes of Health 


Forrest KY, Stuhldreher WL. Prevalence and correlates of vitamin D deficiency in US adults. Nutr Res. 2011 Jan;31(1):48-54. doi: 10.1016/j.nutres.2010.12.001. PMID: 21310306.

Categories: Chronic pain, Physical Therapy